The present invention relates to a magnetron which makes use of the magnetron cathode supporting ceramic stem as a dielectric for a capacitor for a microwave leakage preventive filter.
Recently, an electronic range for dielectrically heating food by generating microwaves has become widespread for domestic use. However, in the event the microwaves generated in the magnetron leak on the power supply side through the lead wires of the cathode of the magnetron, any electronic equipment positioned near the electronic range is adversely affected by noise. In order to prevent this, it has been the practice that a filter, comprising a choke coil and a capacitor, is provided at the input section of the cathode so as to interrupt the microwaves. Such a filter, it is described in Japanese Patent Publication No. 51-7394 with the lead wires of the magnetron supported by the bottom surface of a bottomed-cylindrical ceramic member serving as a cathode supporting stem, and the inner and outer cylindrical surfaces of the ceramic member are metallized to thereby form a capacitor. At the same time, in Japanese Laid-Open Patent Publication No. 50-126160, there is described a structure such that the cathode supporting stem is enclosed by a dielectric cylindrical member, except the terminal section of the cathode and the connection of the cathode terminal and the metallic wall of the tube is metallized to thereby form a through-capacitor. Further, in Japanese Laid-Open Patent Publication No. 55-165547 there is described a structure in which a second cathode support made of a rodlike magnetic body is helically surrounded by a first cathode support so as to form a choke coil, and a tubular dielectric is disposed between these cathode supports and a metallic sealing member surrounding the cathode supports to thereby form a capacitor. In addition, Japanese Laid-Open Patent Publication No. 63-293809 discloses a structure in which a capacitor is formed at the stem portion of the cathode.
FIGS. 1 and 2 respectively show prior art examples described in the above-mentioned Japanese Laid-Open Patent Publication No. 63-293809. In particular, FIG. 1 shows a capacitor in section formed by metallizing the bottom surface of a bottomed-cylindrical ceramic member wherein reference numeral 1 designates a ceramic material as a dielectric, reference numerals 3 and 4 designate cathode leads, reference numerals 11 and 12 designate metallized sections, and reference numeral 7 designates a metallic body forming an enclosure. The metallized section 11 is divided into two regions electrically insulated from each other and electrically connected to the cathode leads 3 and 4, respectively. The metallized section 12 is electrically connected to the metallic body 7 and is kept insulated from the two cathode leads.
FIG. 2 shows a capacitor structure formed at the side surface of a cylindrical ceramic member wherein the metallized section 11 is divided into two regions which are electrically conductive with the cathode leads 3 and 4, respectively. The metallized section 12 is electrically conductive with the metallic body 7 and forms a capacitor together with the metallized section 11, with the ceramic member 13 sandwiched therebetween.
However, of the above prior art examples, those disclosed in Publications Nos. 50-126160 and 55-165547 have complicated structures, each including a number of parts so that they are not suitable for practical use.
Further, those disclosed in Publications Nos. 51-7394 and 63-293809 have problems in respect of their reliability of sealing at the cathode lead section.